Recombinant glycoprotein 63 (Gp63) of Trypanosoma carassii suppresses antimicrobial responses of goldfish (Carassius auratus L.) monocytes and macrophages

We previously reported that proteins secreted by Trypanosoma carassii play a role in evasion of fish host immune responses. To further understand how these parasites survive in the host, we cloned and expressed T. carassii glycoprotein 63 (Tcagp63), and generated a rabbit polyclonal antibody to the recombinant protein (rTcagp63). Tcagp63 was similar to gp63 of other trypanosomes and grouped with Trypanosoma cruzi and Trypanosoma brucei gp63 in phylogenetic analysis. We showed that rTcagp63 down-regulated Aeromonas salmonicida and recombinant goldfish TNFα2-induced production of reactive oxygen and nitrogen intermediates. Macrophages treated with rTcagp63 also exhibited significant reduction in the expression of inducible nitric oxide synthase (iNOS)-A, TNFα-1 and TNFα-2. Recombinant Tcagp63 bound to and was internalised by goldfish macrophages. The Tcagp63 may act by altering the signalling events important in downstream monocyte/macrophage antimicrobial and other cytokine-induced functions. We believe that this is the first report on downregulation of antimicrobial responses by trypanosome gp63.

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► Recombinant Trypanosoma carassii gp63 (rTcagp63) downregulated macrophage antimicrobial responses.
► Pre-incubation of macrophages with rTcagp63 and Aeromonas salmonicida or TNFα2, altered the expression of select immune genes.
► Recombinant Tcagp63 bound and was internalised by macrophages.